Sudanese authorities said Friday they were bracing for the possibility of severe flooding, expected this week, in the capital after rivers swollen by torrential rains in Ethiopia inundated rivers and towns in central Sudan, according to reports.

Some more low-lying sections of Khartoum have already been flooded, they told AFP.

More than 1 billion cubic meters (35 billion cubic feet) of water was expected Friday to sweep into Khartoum, where the Blue and White Nile rivers converge, said the irrigation and water resources ministry.

The river has already reached its highest level in more than 20 years, prompting tens of thousands of people to flee their homes in other parts of Sudan, Africa's largest country. The authorities are urging many others to be prepared to move at short notice.

In 1988, dozens of people were killed and around two million left homeless after the Nile burst its banks, according to Reuters.

The agency said that crops had already been washed away in states such as Sennar, about 300 km (190 miles) south of Khartoum, and at least 35 villages with thousands of inhabitants have been evacuated in Nile River state, about 200 km north of the capital. Authorities in Khartoum have urged citizens to brace themselves for floods in the next few days. In low-lying areas of the capital like the Nile island of Tuti, residents have heaped up sandbags along the riverbank to keep the floods at bay.

The Qatar-based Al Jazeera satellite channel reported on the islanders’ preparations for the expected catastrophe.

"More than one billion cubic meters of water are expected to arrive in Khartoum today (Friday) morning in Khartoum," Malik Bashir, the rapporteur of the emergency room at the ministry of housing and public utilities in Khartoum state, was quoted as saying.

He said the government had provided dozens of trucks and excavators to help heighten embankments as well as pumps to drain rising water.

"The situation, however, is not reassuring and I call upon the citizens and the concerned quarters to exert efforts to overcome the stage of danger," Bashir was quoted as saying.

The fast-moving, muddy water of the Nile rose by some 2.6 cm (more than an inch) in Khartoum from Wednesday to Thursday, with the floods expected to climax some time next week.

On Monday, the International Federation of Red Cross and Red Crescent Societies (IFRC) appealed for 1.3 million Swiss francs ($772,400) in contingency funding in case the Nile floods Khartoum, said Reuters.

The Associated Press reported that UN agencies were gearing up to provide assistance to thousands of Sudanese flood victims.

"They are saying water levels are one meter (yard) higher (in parts of Sudan) than they have been for 20 years," Hamayun Rathor, UN resident coordinator in Khartoum, was quoted as saying, "Some villages have already come under water."

Rathor said in a telephone interview that it was too early to know how much damage the floods had caused. He said UN agencies would meet Saturday to assess the situation and make preparations to deal with outbreaks of disease which are expected to be caused by the floods.

Separately, the Atbara River in northern Sudan has also flooded homes there, while the seasonal Rahad River in Gedaref state has overflowed its banks for the first time in decades, reaching nearby villages.